The present invention relates to a method of producing a cylindrical shell used for fabricating a gas cylinder to contain a gas. More particularly, the present invention relates to such a method in which a billet of circular, transverse cross-section is used to form the cylindrical shell by billet piercing. Even more particularly, the present invention relates to such a method in which the billet is formed of a first section of steel and a second section of liner material so that the cylindrical shell has an outer cylindrical form made of steel and an inner liner insert formed of the liner insert material.
Gas cylinders are widely used in various industries for storing gases. The storage of ultra-high purity gases used within the semiconductor industry is particularly problematical due their corrosive nature. Such corrosion can produce particulate contamination that in turn can produce unacceptable manufacturing defects. For instance, corrosive etching gases such as hydrogen chloride can corrode steel cylinders to produce particulate contaminants. If the resultant particulate material is drawn into a stage of the semiconductor manufacturing process, the product of such stage might be ruined.
Thus, gas cylinders have been specifically designed to maintain the purity of the gas by being fabricated of nickel. As may be appreciated, nickel gas cylinders are prohibitively expensive. Additionally, pure nickel cylinders generally cannot be used where the intended service pressure exceeds 35.15 kg./cm.sup.2. As a result, gas cylinders for high purity gas storage applications are formed with an outer layer of steel for structural integrity and an inner nickel plating for corrosion resistance.
As has been indicated in U.S. Pat. No. 5,330,091, owned by the assignee herein, the electroplating a cylindrical shell of steel with nickel is not a recommended technique for fabricating gas cylinders intended for high purity storage applications because the plating can contain voids or cracks which can trap corrosion products of steel. Therefore, in this prior patent application, circular nickel and steel layers were bonded together by roll bonding or explosive cladding. The resultant two layer circular form is then used as a blank for a cold drawing process to produce the cylindrical shell used in forming the gas cylinder. In a cold drawing process, the blank is formed into a cup-like form with a mandrel and the cup-like form is then extruded by the mandrel, at room temperature, through a series of dies.
The drawback of the process disclosed in U.S. Pat. No. 5,330,091 is that it has not been found to be easily amenable toward the production of large gas cylinders. As will be discussed, the present invention provides a method of forming a seamless, steel cylindrical shell having a corrosion resistant lining that can be used to produce larger gas cylinder sizes than are obtainable by cold drawing production techniques.